Electronic fuel injection system having speed enrichment

ABSTRACT

Fuel is applied to an internal combustion engine for the duration of control pulses produced at a frequency proportional to the speed of the engine. The duration of the control pulses is determined as a function of the amplitude of a bias voltage. A speed voltage unidirectionally varies from a base level at the termination of each preceding control pulse to a peak amplitude at the initiation of each succeeding control pulse. A compensation voltage is substantially constant over the duration of each succeeding control pulse at an amplitude proportional to the peak amplitude of the speed voltage during each preceding cycle. The amplitude of the bias voltage is determined in response to the amplitude of the compensation voltage thereby to define the duration of the control pulses as a function of engine speed.

O United States Paw 1 91 1 1 3,732,852 McGavic 1 May 15, 1973 [54]ELECTRONIC FUEL INJECTION 3,623,461 11/1971 Rabus ..123/32 EA SYSTEMHAVING SPEED ENRICHMENT Primary ExaminerLaurence M. Goodridge [75]Inventor: John P. McGavic, Kokomo, lnd. Aflomey Chnsten et [73]Assignee: General Motors Corporation, [57] ABSTRACT Detroit, Mich. Fuel1s applied to an internal combustion engine for Flledl J ly 1971 theduration of control pulses produced at a frequency [21] APPL No.:158,800 proportional to the speed of the engine. The duration of thecontrol pulses is determined as a function of the amplitude of a biasvoltage. A speed voltage 123/119, 123/140 MC unidirectionally variesfrom a base level at the ter- Q a v .Fozb mination of each precedingcontrol pulse to a peak [58] Field of Search ..l23/32 EA, 32 AE,amplitude at the initiation f each Succeeding control 123/119 pulse. Acompensation voltage is substantially constant over the duration of eachsucceeding control [56] References cued pulse at an amplitudeproportional to the peak am- UNITED STATES PATENTS plitude of the speedvoltage during each preceding cycle. The amplitude of the bias voltageis determmed 1n 3,338,221 8/1967 Scholl ..l23/32 EA re onse to theamplitude of the compensation voltage thereby to define the duration ofthe control pulses as 3:620:l96 11/1971 Wessel .1123/32 EA 3 functionengme Speed 5 Claims, 6 Drawing Figures DULSE 1 GENERATOR SPEEDCOMPENSATOR 84 I INJECTOR DRIVE CIRCUIT PATENTED MAY 1 51973 sum 2 OF 3N a N D N a M W C 1N2 y m N O X a Q n a N f ,0 N E J0 1 ll 3 @255; N

a 73 m w m w/ a o Z a D4. D5 D2 D: A aw i I. u u 6 N D A Z Z 5 5 1; ,5 W5 w 0 E 6 w .l w No m W W im M w w All 1525 M33 z :CZ/NDO g ATTOR NE YELECTRONIC FUEL WJECTION SYSTEM HAVING SPEED ENRIC :1 NT

This invention relates to a fuel supply system for an internalcombustion engine. More particularly, the invention relates to anelectronic fuel injection system for altering the amount of fuel appliedto the engine in response to variations in engine speed.

In one well known type of electronic fuel injection system, controlpulses are produced in synchronization with the rotating speed of theengine. The duration of the control pulses is determined as a functionof at least one engine operating parameter. Further, the duration of thecontrol pulses is at least partially determined as a function of theamplitude of a bias voltage. Fuel is applied to the engine at a constantrate for the duration of each of the control pulses. Thus, since thecontrol pulses are produced at a frequency proportional to the speed ofthe engine, the amount of fuel applied to the engine is inherentlyrelated to engine speed. However, due to certain fuel delivery phenomenarelated to the speed of the engine, such as volumetric efficiency, it isnecessary that more or less fuel be applied to the engine in response tovariations in engine speed. The present invention proposes an electronicfuel injection system which provides the desired speed compensation.

According to one aspect of the invention, a speed voltage comprisessuccessive cycles in which the amplitude of the speed voltage increasesfrom a base level at the termination of each preceding control pulse toa peak level at the initiation of each succeeding control pulse. As aresult, the peak level of the speed voltage is inversely related to thespeed of the engine. The amplitude of the bias voltage is heldsubstantially constant over the duration of each succeeding controlpulse at a bias level determined as a function of the peak level of thespeed voltage during each preceding cycle. Consequently, the duration ofeach of the control pulses is defined in response to engine speed.

In another aspect of the invention, the amplitude of a compensationvoltage increases from a compensation level at the initiation of eachsucceeding control pulse. The compensation level is determined inproportion to the peak level of the speed voltage during each precedingcycle. The increase in the amplitude of the compensation voltage isdefined by a time constant which is relatively long compared to thelongest duration of the control pulses. Hence, the amplitude of thecompensation voltage remains substantially constant at the compensationlevel over the duration of each of the control pulses. The amplitude ofthe bias voltage is determined in response to the amplitude of thecompensation volt- 1 age thereby to define the duration of the controlpulses as a function of engine speed.

As contemplated by another aspect of the invention, the increase in theamplitude of the speed voltage is defined by a time constant such thatthe peak level of the speed voltage is at an upper potential when theengine speed is at a low speed limit and is at a lower potential whenthe engine speed is at a high speed limit. The amplitude of thecompensation voltage is established at a minimum potential when the peaklevel of the speed voltage is at or below the lower potential and isestablished at a maximum potential when the peak level of the speedvoltage is at and above the upper potential. Further, the amplitude ofthe compensation voltage between the maximum potential and the minimumpotential is proportional to the peak level of the speed voltage betweenthe upper potential and the lower potential.

These and other aspects and advantages of the invention may be bestunderstood by reference to the following detailed description of apreferred embodiment when considered in conjunction with theaccompanying drawing.

In the drawing:

FIG. I is a schematic diagram of an electronic fuel injection systemincorporating the principles of the invention.

FIG. 2 is a graphic diagram of several waveforms useful in explainingthe operation of the fuel injection system illustrated in FIG. 1.

FIGS. 3 and 4 are graphic diagrams of certain speed related enginephenomena useful in explaining the principles of the invention.

FIG. 5 is a schematic diagram of a speed compensation circuitincorporating the principles of the invention.

FIG. 6 is a graphic diagram of several waveforms useful in explainingthe operation of the speed compensation circuit illustrated in FIG. 3.

Referring to FIG. I, an internal combustion engine 10 for an automotivevehicle includes a combustion chamber or cylinder 12. A piston 14 ismounted for reciprocation within the cylinder 12. A crankshaft 16 issupported for rotation within the engine 10. A connecting rod 18 ispivotally connected between the piston 14 and the crankshaft 16 forrotating the crankshaft within the engine 10 when the piston 14 isreciprocated within the cylinder 12.

An intake manifold 20 is connected with the cylinder 12 through anintake port 22. An exhaust manifold 24 is connected with the cylinder 12through an exhaust port 26. An intake valve 28 is slidably mountedwithin the top of the cylinder 12 in cooperation with the intake port 22for regilating the entry of combustion ingredients into the cylinder 12from the intake manifold 20. A spark plug 30 is mounted in the top ofthe cylinder 12 for igniting the combustion ingredients within thecylinder 12 when the spark plug 30 is energized. An exhaust valve 32 isslidably mounted in the top of the cylinder 12 in cooperation with theexhaust port 26 for reguiating the exit of combustion products from thecylinder 12 into the exhaust manifold 24. The intake valve 28 and theexhaust valve 32 are driven through a suitable linkage 34 whichconventionally includes rocker arms, lifters, and a camshaft.

An electrical power source is provided by the vehicle battery 36. Anignition switch 38 connects the battery 36 between a power line and aground line 42. When the ignition switch 38 is closed, the battery 36applies a supply voltage to the power line 40. A conventional ignitioncircuit 44 is electrically connected to the power line 40 and ismechanically connected with the crankshaft 16 of the engine Ill.Further, the ignition circuit 44 is connected through a spark cable 46to the spark plug 30. In a conventional manner, the ignition circuit 44energizes the spark plug 30 in synchronization with the rotation of thecrankshaft 16 of the engine 10. Hence, the ignition circuit 44 combineswith the ignition switch 38 and the spark plug 30 to form an ignitionsystem.

A fuel injector 48 includes a housing 50 having a fixed metering orifice52. A plunger 54 is supported within the housing 50 for reciprocationbetween a fully opened position and a fully closed position. In thefully opened position, the forward end of the plunger 54 is opened awayfrom the orifice 52. In the fully closed position, the forward end ofthe plunger 54 is closed against the orifice 52. A bias spring 56 isseated between the rearward end of the plunger 54 and the housing 50 fornormally maintaining the plunger 54 in the fully closed position. Asolenoid or winding 58 is electromagnetically coupled with plunger 54for driving the plunger 54 to the fully opened position against theaction of the bias spring 56 when the winding 58 is energized. The biasspring 56 drives the plunger 54 to the fully closed position when thewinding 58 is deenergized. The fuel injector 48 is mounted on the intakemanifold 20 of the engine for injecting fuel into the intake manifold ata constant flow rate through the metering orifice 52 when the plunger 54is in the fully opened position. Notwithstanding the illustratedstructure, it is to be noted that the fuel injector 48 may be providedby virtually any suitable constant flow rate valve.

A fuel pump 60 is connected to the fuel injector 48 by a conduit 62 andto the vehicle fuel tank 64 by a. conduit 66 for pumping fuel from thefuel tank 64 to the fuel injector 48. Preferably, the fuel pump 60 isconnected to the power line 40 to be electrically driven from thevehicle battery 36. Alternately, the fuel pump 60 could be connected tothe crankshaft 16 to be mechanically driven from the engine 10. Apressure regulator 68 is connected to the conduit 62 by a conduit 70 andis connected to the fuel tank 64 by a conduit 72 for defining thepressure of the fuel applied to the fuel injector 48. Thus, the fuelinjector 48 combines with the fuel tank 64, the fuel pump 60 and thepressure regulator 68 to form a fuel supply system.

A throttle valve 74 is rotatably mounted within the intake manifold 20for regulating the flow of air into the intake manifold 20 in accordancewith the position of the throttle valve 74. The throttle valve 74 isconnected through a suitable linkage 76 with the vehicle acceleratorpedal 78. The accelerator pedal 78 is pivotably mounted on a referencesurface for movement against the action of a compression spring 79seated between the accelerator pedal 78 and the reference surface. Asthe accelerator pedal 78 is depressed, the throttle valve 74 is moved toa more opened position to increase the flow of air into the intakemanifold 20. Conversely, as the accelerator pedal 78 is released, thethrottle valve 74 is moved to a less opened position to decrease theflow of air into the intake manifold 20.

In operation, fuel and air are combined within the intake manifold 20 toform an air/fuel mixture. The fuel is injected into the intake manifold20 at a constant flow rate by the fuel injector 48 in response toenergization. The precise amount of fuel deposited within the intakemanifold 20 is regulated by a fuel supply control system which will bedescribed later. The air enters the intake manifold 20 from the airintake system (not shown) which conventionally includes an air filter.The precise amount of air admitted into the intake manifold 20 isdetermined by the position of the throttle valve 74. as previouslydescribed, the position of the accelerator pedal 78 controls theposition of the throttle valve 74.

As the piston 14 initially moves downward within the cylinder 12 on theintake stroke, the intake valve 28 is opened away from the intake port22 and the exhaust valve 32 is closed against the exhaust port 26.Accordingly, combustion ingredients in the form of the air/fuel mixturewithin the intake manifold 20 are drawn by negative pressure through theintake port 22 into the cylinder 12. As the piston 14 subsequently movesupward within the cylinder 12 on the compression stroke, the intakevalve 28 is closed against the intake port 22 so that the air/fuelmixture is compressed between the top of the piston 14 and the top ofthe cylinder 12. When the piston 14 reaches the end of its upward travelon the compression stroke, the spark plug 30 is energized by theignition circuit 44 to ignite the air/fuel mixture. The ignition of theair/fuel mixture starts a combustion reaction which drives the piston 14downward within the cylinder 12 on the power stroke. As the piston 14again moves upward within the cylinder 12 on the exhaust stroke, theexhaust valve 32 is opened away from the exhaust port 26. As a result,the combustion products in the form of various exhaust gases are pushedby positive pressure out of the cylinder 12 through the exhaust port 26into the exhaust manifold 24. The exhaust gases pass out of the exhaustmanifold 24 into the exhaust system (not shown) which conventionallyincludes a muffler and an exhaust pipe.

Although the structure and operation of only a single combustion chamberor cylinder 12 has been described, it will be readily appreciated thatthe illustrated internal combustion engine 10 may include additionalcylinders 12 as desired. Similarly, additional fuel injectors 48 may beprovided as required. However, as long as the fuel injectors 48 aremounted on the intake manifold 20, the number of additional fuelinjectors 48 need not necessarily bear any fixed relation to the numberof additional cylinders 12. Alternately, the fuel injector 48 may bedirectly mounted on the cylinder 12 so as to inject fuel directly intothe cylinder 12. In such instance, the number of additional fuelinjectors 48 would necessarily equal the number of additional cylinders12. At this point, it is to be understood that the illustrated internalcombustion engine 10, together with all of its associated equipment, isshown only to facilitate a more complete understanding of the inventiveelectronic control system.

A timing pulse generator 80 is connected with the crankshaft 16 fordeveloping rectangular timing pulses having a frequency which isproportional to and synchronized with the rotating speed of thecrankshaft 16. The rectangular timing pulses are applied to a timingline 82. preferably, the timing pulse generator 80 is some type ofinductive speed transducer coupled with a bistable circuit. However, thetiming pulse generator 80 may be provided by virtually any suitablepulse producing device such as a multiple contact rotary switch.

An injector drive circuit 84 is connected to the power line 40 and tothe timing line 82. Further, the injector drive circuit 84 is connectedthrough an injection line 8610 the fuel injector 48. The injector drivecircuit 84 is responsive to the timing pulses produced by the timingpulse generator 80 to energize the fuel injector valve 48 insynchronization with the rotating speed or frequency of the crankshaft16 in much the same manner as the ignition circuit 44 energizes thespark plug 3%). The time period for which the fuel injector 48 isenergized by the drive circuit 84 is determined by the length orduration of rectangular control pulses produced by a modulator orcontrol pulse generator 88 which will be more fully described later. Thecontrol pulses are applied by the control pulse generator 88 to theinjector drive circuit 84 over a control line 90 in synchronization withthe timing pulses produced by the timing pulse generator $0. In otherwords, the injector drive circuit 84 is responsive to the coincidence ofa timing pulse and a control pulse to energize the fuel in jector 48 forthe length or duration of the control pulse.

The injector drive circuit 84 may be virtually any amplifier circuitcapable of logically executing the desired coincident pulse operation.However, where additional fuel injectors 48 are provided, it may benecessary that the injector drive circuit 84 also select which one orones of the fuel injectors 48 are to be energized in response to eachrespective timing pulse. As an example, the fuel injectors 48 may bedivided into separate groups which are successively energized inresponse to successive ones of the timing pulses. Conversely, the timingpulses may be applied to operate a counter circuit or a logic circuitwhich individually selects the fuel injectors 48 for energization.

The control pulse generator 88 includes a monostable multivibrator orblocking oscillator 92. The blocking oscillator 92 includes a controltransducer 94 having a primary winding 96 and a secondary winding 98which are variably inductively coupled through a movable magnetizablecore 100. The deeper the core 100 is inserted into the primary andsecondary windings 96 and 98, the greater the inductive coupling betweenthe primary winding 96 and the secondary winding 98. The movable core100 is mechanically connected through a suitable linkage 102 with apressure sensor 1114. The pressure sensor 104 communicates with theintake manifold 20 of the engine downstream from the throttle 74 througha conduit 106 for monitoring the negative pressure or vacuum within theintake manifold 20. The pressure sensor 104 moves the core 1 within thecontrol transducer 94 to regulate the inductive coupling between theprimary and secondary windings 96 and 98 as an inverse function of thevacuum within the intake manifold 20. Therefore, as the vacuum withinthe intake manifold 20 decreases in response to the opening of thethrottle 74, the core 100 is inserted deeper within the controltransducer 94 to proportionately increase the inductive coupling betweenthe primary winding 96 and the secondary winding 98.

The monostable multivibrator or blocking oscillator 92 further includesa pair of NPN Junction transistors 108 and 110. The primary winding 96is connected from the collector electrode of the transistor 110 througha limiting resistor 112 to the power line The secondary winding 98 isconnected from an input junction 114 through a steering diode 116 to abias junction 1 18 between a pair of biasing resistors 120 and 122 whichare connected in series between the power line 40 and the ground line42. A biasing resistor 124 is connected between the junction 114 and thepower line 40. The base electrode of the transistor 108 is connectedthrough a steering diode 126 to the junction 114. The emitter electrodesof the transistors 1 and 110 are connected directly to the ground line42. The

collector electrode of the transistor 108 is connected through a biasingresistor 128 to the power line 40 and is connected through a biasingresistor 1.30 to the base electrode of the transistor 110.

Further, the control pulse generator includes a differentiator 132provided by a capacitor 134 and a pair of resistors 136 and 138. Theresistors 136 and 1.38 are connected in series between the power line 40and the ground line 42. The capacitor 134 is connected from the timingline 82 to a junction 14'!) between the resistors 136 and 138. Asteering diode 142 is connected from the junction 140 between theresistors 136 and 138 to the input junction 114. In operation, timingpulses are applied through the timing line 82 to the differentiator 132.The differentiator 132 develops negative trigger pulses at the junction140 in response to the timing pulses. The diode 142 applies the triggerpulses from the junction 140 to the junction 114.

Referring to FIGS. 1 and 2, the monostable multivibrator or blockingoscillator 92 switches from a stable state to an unstable state inresponse to a decrease in the voltage at the input junction 114 below apredetermined threshold potential P,. The voltage appearing at thejunction 114 comprises the combination of a pressure voltage A and abias voltage B as shown in FIG. 2b. The pressure voltage A is providedby the control transducer 94 and the bias voltage B is provided by abias voltage network including the resistors 120, 122 and 124. When thevoltage at the junction 114 is above the threshold potential P,, thetransistor 108 is rendered fully conductive through the coupling actionof the diode 126 and the transistor is rendered fully nonconductivethrough the biasing action of the resistor 130.

With the pressure voltage A absent, the bias voltage B provided by theresistors 120, 122 and 124 is at a normal level L which maintains thevoltage at the junction 1 14 above the threshold potential P, so thatthe transistor 1118 is normally turned on and the transistor 110 isnormally turned off. However, when a negative trigger pulse arrives atthe junction 114, the voltage at the junction 114 immediately dropsbelow the threshold potential P Consequently, the transistor 108 isturned off through the coupling action of the diode 126, and thetransistor 110 is turned on through the biasing action of the resistors128 and 130. With the transistor 110 turned on, a control pulse C, asshown in FIG. 2a, is initiated on the control line 90. The level of thecontrol pulse C is defined by the saturation voltage drop of thetransistor 110.

With the transistor 110 turned on, a current is established in theprimary winding 96 of the control transducer 94 to develop a pressurevoltage A across the secondary winding 98 of the control transducer 94.The pressure voltage A initially instantaneously decreases from thelevel of the bias voltage B to a peak lower level and subsequentlygradually decreases back to the level of the bias voltage B. Thepressure voltage A is coupled through the diode 116 to the junction 114to hold the voltage at the junction 114 below the threshold potential PConsequently, the transistor 108 remains turned off and the transistor110 remains turned The peak lower level of the pressure voltage A isdetermined by the inductive coupling between the primary and secondarywindings 96 and 98 of the control transducer 94. In turn, the inductivecoupling between the primary and secondary windings 96 and 98 is definedby the position of the movable core 100. The rate at which the pressurevoltage A increases from the peak lower level back to the normal levelL,, of the bias voltage B is determined by the L/R time constant of theprimary winding and the limin'ng resistor 112. As

the pressure voltage A increases, the voltage at the junction114leventually rises above the threshold potential P Accordingly, thetransistor 1% is turned on and the transistor 110 is turned off. Withthe transistor 108 turned off, the control pulse C on the control line90 is terminated.

Thus, the duration of the control pulses occurring on the control line90 is determined by the combination of the pressure voltage A and thebias voltage 8. More particularly, the length of the control pulses C isinversely related to the amplitude of the bias voltage B. Hence, if theamplitude of the bias voltage B is decreased, the length of the controlpulses C is increased. Alternately, if the amplitude of the bias voltageis increased, the length of the control pulses C is decreased. However,assuming for the moment that the bias voltage B is constant, theduration of the control pulses C is defined by the pressure sensor 1 andthe control transducer 94 as an inverse function of the vacuum withinthe intake manifold 20 of the engine 10.

As previously described, the frequency of the control pulses C producedby the control pulse generator is proportional to the speed of theengine 10. As a result, the amount of fuel applied to the engine MB isinherently a function of engine speed. However, due to certain speedrelated fuel delivery phenomena, such as volumetric efficiency, it isnecessary that the normal fuel quantity be changed in response tovariations in engine speed. The effects of these fuel delivery phenomenamay be best understood by reference to FIG. 3, which illustrates a setof typical fuel demand curves D -D assuming the engine comprises eightcylinders. The fuel demand curves D -D each represent a graph of fuelquantity versus engine speed at different constant manifold pressures.Since the quantity of fuel delivered to the engine llll is directlyrelated to the length of the control pulses C, the ordinate of the graphalso represents control pulse length.

In general, the fuel demand curves D -d each exhibit one transitionpoint at approximately the same lower speed limit N and anothertransition point at approximately the same upper speed limit N Below thelower speed limit N the fuel demand curves D,D are each relativelyconstant at different minimum levels. Between the lower speed limit Nand the upper speed limit N the fuel demand curves D,D each graduallyincrease from the different minimum levels to different maximum levels.Above the upper speed limit N the fuel demand curves D D are relativelyconstant at the different maximum levels. At very high engine speeds andhigh engine loads, the fuel demand curves d -D exhibit some roll-off.However, for purposes of the present invention, this minor roll-off maybe neglected.

In order to achieve optimum operation of the engine 10, the fuel demandcurves D -ll, indicate that the amount of fuel normally applied to theengine Ml must be compensated for variations in engine speed. Morespecifically, extra fuel should be added to the normal fuel quantity inaccordance with a speed compensation curve X, which is illustrated inFIG. 41. The speed compensation curve X represents a graph of thedesired percentage increase in the normal fuel quantity versus enginespeed. As might be expected, the fuel compensation curve X is a generalapproximation of each of the respective fuel demand curves D -D.,.

According to the fuel compensation curve X, an increasing amount ofextra fuel should be added to the normal fuel quantity in response toincreasing engine speed between the lower speed limit N and the upperspeed limit N That is, the normal duration of the control pulses C asdetermined by the pressure in the intake manifold 20 should be extendedby a percentage which increases with increasing engine speed between thelower speed limit N and the upper speed limit N However, when the speedof the engine 10 is below the lower speed limit N a constant minimumamount of fuel should be added to the normal fuel quantity. Similarly,when the speed of the engine 10 is above the upper speed limit N aconstant maximum amount of fuel should be added to the normal fuelquantity. In other words, the normal duration of the control pulses C asdetermined by the pressure in the intake manifold 20 should be increasedby a constant minimum percentage when the engine speed is below thelower speed limit N and by a constant maximum percentage when the enginespeed is above the upper speed limit N The present invention provides anelectronic fuel injection system including a speed compensator 144 forvarying the amount of fuel delivered to the engine in accordance withthe speed compensation curve X. The speed compensator 144 includes aninput connected over the control line to the output transistor of thecontrol pulse generator 88 and an output connected over an output line1145 to the junction 118 in the control pulse generator 88. However, itwill be appreciated that an engine different from the engine 10, andhaving fuel demand curves different from the fuel demand curves D wouldnecessarily have a speed compensation curve different from the speedcompensation curve X. Hence, some engines may require a speedcompensation curve exactly opposite to the speed compensation curve X.That is, a speed compensation curve which decreases from a maximum levelat the lower speed limit N to a minimum level at the upper speed limit NAs will become more apparent later, the speed compensator 144 is capableof provid ing either type of speed compensation curve.

FIG. 5 illustrates a preferred embodiment of the speed compensator 144-including a speed voltage generator 146, a compensation voltagegenerator 148 and a bias voltage modifier 1150. FIG. 6 illustrates theoperation of the speed compensation M4 at three different engine speedsN N and n;,. In FIG. 6a, the engine speed N is below the lower speedlimit N In FIG. 6b, the eng'ne speed N is midway between the lower speedlimit N and the upper speed limit N In FIG. 60, the engine speed N isabove the upper speed limit N Referring to FIGS. 5 and 6, a speedvoltage S is developed across a capacitor 152 at a junction 153.Further, a compensation voltage K is developed across a capacitor 154 ata junction 155. As shown in FIG. 5, the speed voltage S is measuredbetween the junction 153 and the ground line 42 while the compensationvoltage is measured between the junction 155 and the ground line 42.Hence, as the speed voltage S and the compensation voltage K increasesin magnitude across the respective capacitors 152 and 154, the absoluteamplitude of the voltages S and K declines from the potential of thepower line 44) toward the potential of the ground line 42.

The speed voltage generator 146 produces the speed voltage S at thejunction 153.. The amplitude of the speed voltage S unidirectionallyvaries from a base level L, at the termination of each preceding controlpulse C to a peak level L, at the initiation of each of each succeedingcontrol pulse C. As a result, the peak amplitude of the speed voltage Sis inversely proportional to the speed of the engine 10. Thecompensation voltage generator 148 produces the compensation voltage Kat the junction 155. The amplitude of the compensation voltage K issubstantially constant at a compensation level L, which is proportionalto the peak level L, of the speed voltage S. The bias voltage modifier150 shifts the amplitude of the bias voltage B from the normal level L,in response to the amplitude of the compensation voltage K to define theduration of the control pulses C as a function of the speed of theengine 10.

The speed voltage generator 146 includes the capacitor 152 connectedbetween the power line 40 and the junction 153. A switching device 158is provided by a PNP junction transistor 160 and an NPN junctiontransistor 162. The emitter electrode'of the transistor 160 and thecollector electrode of the transistor 162 are connected together to thepower line 40. The collector electrode of the transistor 160 isconnected directly to the base electrode of the transistor 162. Theemitter electrode of the transistor 162 is connected directly to thejunction 152. The base electrode of the transistor 160 is connectedthrough a biasing resistor 163 to the power line 40 and through abiasing resistor 164 over the control line 90 to the control pulsegenerator 88. In addition, a variable limiting resistor 166 is connectedbetween the junction 153 and the ground line 42.

As previously described, the speed voltage S is developed across thecapacitor 152 at the junction 153. In response to the initiation orleading edge of each control pulse C, the transistors 160 and 162 of theswitching device 158 are rendered fully conductive. With the switchingdevice 158 turned on, the capacitor 152 is discharged through thetransistors 160 and 162 to effectively clamp the amplitude of the speedvoltage S at the base level L, which is approximately equal to thesupply potential on the power line 40. In response to the termination ortrailing edge of each control pulse C, the transistors 160 and 162 ofthe switching device 158 are rendered fully nonconductive. With theswitching device 158 turned off, the capacitor 152 charges through theresistor 166. As a result, the amplitude of the speed voltage Sincreases from the base level L, in accordance with the RC time constantprovided by the capacitor 152 and the resistor 166. In response to theinitiation or leading edge of the next control pulse C, the switchingdevice 158 is again turned on to clamp the amplitude of the speedvoltage S at the base level L,.

Accordingly, the speed voltage S comprises successive cycles duringwhich the amplitude of the speed voltage S reaches a peak level L, atthe initiation of each succeeding control pulse C. Due to the timeconstant provided by the capacitor 152 and the resistor 166, theamplitude of the speed voltage S increases in a fairly linear manner.Hence, the peak amplitude or peak level L, of the speed voltage S isdirectly related to a time period T, extending from the termination ofeach preceding control pulse C to the initiation of each succeedingcontrol pulse C. In turn, the time period T, is inversely related to thefrequency of the control pulses C in a nonlinear manner. That is, if thefrequency of the control pulses C increases at a fixed rate,

the duration of the time period T, decreases at an ever increasing rate.As a result, the peak amplitude of the speed voltage C is inverselyrelated to the speed of the engine 10 in the same nonlinear manner.

The time constant provided by the capacitor 152 and the resistor 166 isadjusted by varying the resistance of the resistor 166. In particular,this time constant is set so that the peak amplitude of the speedvoltage S across the capacitor 152 is at an upper potential P, when theengine speed is at the lower speed limit N, and the peak amplitude ofthe speed voltage S is at a lower potential P, when the engine speed isat the upper speed limit N,. In other words, the peak level L, of thespeed voltage S equals the upper potential P, when the engine speed isat the lower limit N, and the peak level L, of the speed voltage Sequals the lower potential P, when the engine speed is at the upperspeed limit N,. Hence, with the engine 10 at the speed N, as shown inFIG. 6a, the peak level L, of the speed voltage S is above the upperpotential P,. With the engine 10 at the speed N as shown in FIG. 6b, thepeak level L, of the speed voltage S is midway between the upperpotential P, and the lower potential P,. Further, with the engine 10 atthe speed N, as shown in FIG. 60, the peak level L, of the speed voltageS is below the lower potential P,. The significance of the relationshipbetween the amplitude of the speed voltage S and the upper and lowerpotentials P, and P, will become more apparent later.

The compensation voltage generator 148 includes the capacitor 154connected between the power line 40 and the junction 155. A limitingresistor 170 is connected in series with a temperature compensatingdiode 171 between the power line 40 and the junction 155. A differentialamplifier 172 includes NPN junction transistors 174, 176 and 178. Thebase electrode of the transistor 174 is connected to a junction 180. Abiasing resistor 182 is connected between the power line 40 and thejunction 180. A temperature compensating diode 184 is connected betweenthe junction and the ground line 42. The emitter electrode of thetransistor 174 is connected directly to the ground line 42. Thecollector electrode of the transistor 174 is connected to a junction186. A pair of biasing resistors 188 and 190 are connected between thejunction 186 and the emitter electrodes of the transistors 176 and 178,respectively. The base electrode of the transistor 176 is connected tothe junction 152. The base electrode of the transistor 178 is connectedto a junction 192. A pair of biasing resistors 194 and 196 are connectedfrom the junction 192 to the power line 40 and the ground line 42,respectively. The collector electrode of the transistor 176 is connecteddirectly to the power line 40. The collector electrode of the transistor178 is connected directly to the junction 154.

In conjunction with the biasing resistor 182 and the temperaturecompensating diode 184, the transistor 174 provides a constant currentsink for the transistors 176 and 178 of the differential amplifier 172.The transistors 176 and 178 form a balanced differential pair forgradually switching between first and second conductive conditions inresponse to the amplitude of the speed voltage S at the junction 152. Asthe amplitude of the speed voltage S increases from the base level L,toward the lower potential P,, the transistor 176 is rendered fullyconductive and the transistor 178 is rendered fully nonconductive. Thisis the first conductive condition of reference differential amplifier172. when the amplitude of the speed voltage S increases through thelower potential P the transistor 176 begins to turn off and thetransistor 178 begins to turn on. As the amplitude of the speed voltageS proportionately increases between the lower level P and'the upperlevel P the transistor 176 is correspondingly rendered less conductivewhile the transistor 178 is correspondingly rendered more conductive.When the amplitude of the speed voltage S increases through the upperpotential P the transistor 176 is rendered fully nonconductive and thetransistor 178 is rendered fully conductive. This is the secondconductive condition of the differential amplifier 172. As the amplitudeof the speed voltage S increases from the upper potential P to the peaklevel L,,, the differential amplifier 172 remains in the secondconductive condition.

The upper and lower potentials P and P of the speed voltage S aredetermined by the biasing resistors 188, 190, 194 and 196. Preferably,the resistors 188 and 190 have a like resistance while the resistors 194and 196 have a like resistance. However, this constraint is notcritical. The biasing resistors 194 and 196 form a voltage dividernetwork for developing a reference voltage R at the junction 192. Theamplitude of the reference voltage R is substantially constant at areference potential P, defined relative to the supply potential on thepower line 40 by the ratio of the resistances of the resistors 194 and196. Similarly, ratio of the resistances of the resistors 188 and 190defines the upper and lower potentials P and P with respect to thereference potential P Therefore, since the upper and lower potentials Pand P of the speed voltage S are defined by relative resistance ratiosrather than absolute resistance values, the biasing resistors 188, 190,194 and 196 may conveniently be formed within an integrated circuitwhich requires no external calibration except for an adjustment of thevariable resistor 166.

During each control pulse C, the differential amplifier 172 is reset tothe first conductive condition since the amplitude of the speed voltageS at the base level L,,. At the initiation of each succeeding controlpulse C, the conductive position of the differential amplifier 172between the first and second conductive conditions is dependent upon thepotential position of the peak amplitude or peak level L of the speedvoltage S relative to the upper and lower potentials P and P When thepeak level L of the speed voltage S is above the upper potential P, asshown in FIG. 6a, the differential amplifier 172 is fully switched tothe second conductive condition during each cycle of the speed voltageS. When the peak level L,, of the speed voltage S is midway between theupper and lower potentials P and P as shown in FIG. 6b, the differentialamplifier 172 is halfswitched between the first and second conductiveconditions during each cycle of the speed voltage S. When the peak levelL,, of the speed voltage S is below the lower potential P, as shown inFIG. 6c, the differential amplifier 172 remains in the first conductivecondition during each cycle of the speed voltage S. v

The compensation voltage k is developed across the capacitor 154 at thejunction 155. During each control pulse C, the transistor 178 in thedifferential amplifier 172 is rendered fully nonconductive. With thetransistor 178 turned off, the capacitor 154 is discharged through theresistor 170. As a result, the amplitude of the compensation voltage Kdecreases in accordance with the RC time constant provided by thecapacitor 154 and the resistor 170. However, since this time constant isrelatively long compared to the longest duration of the control pulsesC, the amplitude of the compensation voltage K remains substantiallyconstant at a compensation level L, over the duration of each succeedingcontrol pulse C. Therefore, the amplitude of the compensation voltage Kis completely independent of variations in the duration of the controlpulses C due to pressure changes in the intake manifold 20 of the engine10.

Further, the time constant provided by the capacitor 154 and theresistor 170 is relatively short compared to the maximumrate-of-increase in the speed of the engine 10 as the throttle valve 74is suddenly moved to the fully opened position. Consequently, the compensation level L of the compensation voltage K is defined by theconduction of the transistor 178 in the differential amplifier 172 atthe initiation of each succeeding control pulse C. Hence, when thedifferential amplifier 172 is in the second conductive condition at thetermination of a control pulse C, the amplitude of the compensationvoltage K is at a maximum potential P When the differential amplifier172 is in the first conductive condition at the termination of thecontrol pulse C, the amplitude of the compensation voltage K is at aminimum potential P In addition, as the differential amplifier 172 isproportionately switched between the first and secondconductive-conditions at the termination of the control pulse C, theamplitude of the compensation voltage K is correspondingly definedbetween the maximum and minimum potentials P, and P Accordingly, thecompensation level L of the compensation voltage K is directly relatedto the peak level L of the speed voltage S. When the peak amplitude ofthe speed voltage S is at or above the upper potential p the amplitudeof the compensation voltage K is at the maximum potential P Conversely,when the peak amplitude of the speed voltage S is at or below the lowerpotential P the amplitude of the compensation voltage K is at theminimum potential P Further the potential position of the amplitude ofthe compensation voltage K relative to the maximum and minimumpotentials p and P is proportional to the potential position of the peakamplitude of the speed voltage S relative to the upper and lowerpotentials P and P Thus, with the peak level L of the speed voltage Sbelow the lower potential P as shown in FIG. 6a, the compensation levelL, of the compensation voltage K is equal to the maximum potential PWith the peak level L of the speed voltage S equal to the referencepotential P, as shown in FIG. 6b the compensation Level L, of thecompensation voltage K is midway between the maximum and minimumpotentials P and p,,. Finally, with the peak level L, of the speedvoltage 5 below the lower potential as shown in FIG. 6c, thecompensation level L of the compensation voltage K is equal to theminimum potential P P,.

The bias voltage modifier include a constant current source 198 and aconstant current sink 200. The constant current source 198 includes aPNP junction transistor 202 and an NPN junction transistor 204. Theemitter electrode of the transistor 202 and the collector electrode ofthe transistor 204 are connected through a limiting resistor 206 to thepower line 40. The collector electrode of the transistor 202 isconnected directly to the base electrode of the transistor 204. The baseelectrode of the transistor 202 is connected directly to the junction155. The emitter electrode of the transistor 204 is connected to ajunction 208 in the current sink 204).

The constant current sink 200 includes an NPN junction transistor 210.The base electrode of the transistor 210 is connected directly to thejunction 208. The emitter electrode of the transistor 210 is connectedthrough a limiting resistor 212 to the ground line 42. A biasingresistor 214 is connected in series with the temperature compensatingdiode 216 between the junction 208 and the ground line 42. The collectorelectrode of the transistor 210 is connected directly to the junction118 in the control pulse generator 88.

In the constant current source 198, the transistors 202 ad 204 arerendered conductive in response to the compensation voltage K toestablish a compensation current through the resistor 206. The magnitudeof the compensation current is directly related to the amplitude of thecompensation voltage K developed across the capacitor 168. That is, asthe amplitude of the compensation voltage K increases, the magnitude ofthe compensation current I increases. In the constant current sink 200,the transistor 210 is rendered conductive in response to thecompensation current through the resistor 214 and the diode 216. As aresult, the transistor 210 defines a bias current through theresistor'2l2 having a magnitude directly proportional to the magnitudeof the compensation current. The bias current is drawn out of theconjunction 118 in the control pulse generator 88 through the outputline 145. Accordingly, the current sink 200 effectively appears as avariable resistance connected between the junction 118 and the groundline 42.

Referring to FIGS. 1, 2 and 6, the length of the control pulses Cproduced by the control pulse generator 88 is inversely related to theamplitude of the bias voltage B at the junction 114. Further, theamplitude of the bias voltage B is inversely related to the magnitude ofthe bias current at the junction 118. In turn, the magnitude of the biascurrent is a direct function of the amplitude of the compensationvoltage K at the junction 154. When the speed of the engine 10 is at orbelow the lower speed limit N the amplitude of the bias voltage B isshifted from the normal level L by a minimum amount. Conversely, whenthe speed of the engine 10 is at or above the upper speed limit N,,, theamplitude of the bias voltage B is shifted from the normal level L by amaximum amount. Further, as the speed of the engine 10 isproportionately changed between the upper and lower speed limits N,, andn the amplitude of the bias voltage is proportionately shifted betweenthe maximum and minimum amounts. In this manner, the length of thecontrol pulses C is varied to compensate the amount of fuel applied tothe engine 10 for variations in engine speed.

It will now be appreciated that the present invention provides a simplebut effective speed compensator for an electronic fuel injection system.In particular, the amount of speed compensation produced by theinvention is substantially independent of control pulse length asdetermined by other factors. However, it is to be understood that theillustrated embodiment of the invention is shown for demonstrativepurposes only. Accordingly, various modifications and alterations may bemade to the illustrated embodiment without departing from the spirit andscope of the invention.

What is claimed is:

1. In an internal combustion engine system including control pulsegenerator means for producing control pulses at a frequency proportionalto the speed of the engine, the control pulse generator means includingbias voltage generator means for defining the duration of the controlpulses as a function of the amplitude of the bias voltage; and fuelinjection means connected between the control pulse generator means andthe engine for applying fuel to the engine for the duration of each ofthe control pulses; the combination comprising: speed voltage generatormeans connected to the control pulse generator means for producing aspeed voltage having an amplitude which unidirectionally varies from abase level at the termination of each preceding control pulse to a peaklevel at the initiation of each succeeding control pulse; and meansconnected between the speed voltage generator means and the bias voltagegenerator means for maintaining the amplitude of the bias voltagesubstantially constant at a level proportional to the peak level of thespeed voltage thereby to define the duration of the control pulses inresponse to the speed of the engine.

2. In an internal combustion engine system including control pulsegenerator means for producing control pulses at a frequency proportionalto the speed of the engine, the control pulse generator means includingbias voltage generator means for defining the duration of the controlpulses as a function of the amplitude of a bias voltage; and fuelinjection means connected between the control pulse generator means andthe en'- gine for applying fuel to the engine for the duration of eachof the control pulses; the combination comprising: speed voltagegenerator means connected to the con trol pulse generator means forproducing a speed voltage having successive cycles during which theamplitude of the speed voltage unidirectionally varies from a base levelat the termination of each preceding control pulse to a peak level atthe initiation of each succeeding control pulse; compensation voltagegenerator means connected to the speed voltage generator means forproducing a compensation voltage having an amplitude which issubstantially constant over the duration of each succeeding controlpulse at a level proportional to the peak level of the speed voltageduring each preceding cycle; and bias voltage modifier means connectedbetween the compensation voltage generator means and the bias voltagegenerator means for defining the amplitude of the bias voltage as afunction of the amplitude of the compensation voltage thereby todetermine the duration of the control pulses in response to the speed ofthe engine.

3. In an internal combustion engine system including control pulsegenerator means for producing control pulses in synchronization with thespeed of the engine, the control pulse generator means including biasvoltage generator means for defining the duration of the control pulsesas a function of the amplitude of a bias voltage; and fuel injectionmeans connected between the control pulse generator means and the enginefor applying fuel to the engine for the duration of each of the controlpulses; the combination comprising: speed voltage generator meansconnected to the control pulse generator means for producing a speedvoltage which varies from a base level at the termination of eachpreceding control pulse, the speed voltage generator means including anRC network having a time constant for defining the amplitude of thespeed voltage in accordance with the time constant which is relativelyshort compared to the shortest duration between each of the controlpulses; compensation voltage generator means connected to the speedvoltage generator means for producing a compensation voltage whichvaries from a base level proportional to the peak level of the speedvoltage at the initiation of each succeeding control pulse, thecompensation voltage generator means including an RC network having atime constant for defining the amplitude of the compensation voltage inaccordance with the time constant which is relatively long compared tothe longest duration of each of the control pulses; and bias voltagemodifier means connected be tween the compensation voltage generatormeans and the bias voltage generator means for controlling the amplitudeof the bias voltage in response to the amplitude of the compensationvoltage thereby to define the duration of the control pulses as afunction of the speed of the engine.

4. In an internal combustion engine system including control pulsegenerator means for producing control pulses at a frequency proportionalto the speed of the engine, the control pulse generator means includingbias voltage generator means for defining the duration of each of thecontrol pulses as a function of the level of the bias voltage; and fuelinjection means connected between the control pulse generator means andthe engine for applying fuel to the engine for the duration of each ofthe control pulse; the combination comprising: speed voltage generatormeans connected to the control pulse generator means for producing aspeed voltage which varies from a base level at the termination of eachpreceding control pulse to a peak level at the initiation of eachsucceeding control pulse so that the peak level of the speed voltage isinversely related to the speed of the engine, the speed voltagegenerator means including an RC network having a time constant fordefining the amplitude of the speed voltage such that the peak leveloccurs at an upper potential when the engine speed is at a lower limitand occurs at a lower potential when the engine speed is at an upperlimit; compensation voltage generator means connected to the speedvoltage generator means for producing a compensation voltage whichvaries from a base level at the initiation of each succeeding controlpulse, the compensation voltage generator means including a voltagelevel converter for defining the base level of the compensation voltagerelative to a maximum potential and a minimum potential as the peaklevel of the speed voltage is defined relative to the upper potentialand the lower potential, the compensation voltage generator meansfurther including an RC network having a time constant for definingtheamplitude of the compensation voltage substantially constant at the baselevel over the duration of each succeeding control pulse; and biasvoltage modifier means connected between the compensation voltagegenerator means and the bias voltage generator means for shifting theamplitude of the bias voltage in proportion to the amplitude of thecompensation voltage thereby to define the duration of the controlpulses as a function of the speed of the engine.

5. In an internal combustion engine system including control pulsegenerator means for producing control pulses at a frequency proportionalto the speed of the engine, the control pulse generator means includingbias voltage generator means for defining the duration of the controlpulses as a function of the amplitude of a bias voltage; and fuelinjection means connected between the control pulse generator means andthe engine for applying fuel to the engine for the duration of each ofthe control pulses; the combination comprisin g: speed voltage generatormeans connected to the control pulse generator means and including acapacitor for developing a speed voltage thereacross, discharging meansconnected to the capacitor for discharging the capacitor from theinitiation of each preceding control pulse until the termination of eachpreceding control pulse to clamp the speed voltage at a base level, andcharging means connected to the capacitor for charging the capacitorfrom the termination of each preceding control pulse to the initiationof each succeeding control pulse according to a relatively short timeconstant to increase the speed voltage from the base level to a peaklevel which is at an upper potential when the engine speed is at a lowlimit and which is at a lower potential when the engine speed is at ahigh limit; compensation voltage generator means connected to the speedvoltage generator means and including a capacitor for developing acompensation voltage thereacross, charging means connected to thecapacitor for charging the capacitor from the termination of eachpreceding control pulse until the initiation of each succeeding controlpulse to clamp the compensation voltage at a base level defined relativeto a maximum potential and a minimum potential as the peak level of thespeed voltage is defined relative to the upper potential and the lowerpotential, and discharging means connected to the capacitor forcontinually discharging the capacitor according to a relatively longtime constant to maintain the compensation voltage substantiallyconstant at the base level over the duration of each succeeding controlpulse; and the bias voltage modifier means connected between thecompensation voltage generator means and the bias voltage generatormeans for defining the amplitude of the bias voltage in response to theamplitude of the compensation voltage thereby to determine the durationof the control pulses as a function of engine speed.

1. In an internal combustion engine system including control pulsegenerator means for producing control pulses at a frequency proportionalto the speed of the engine, the control pulse generator means includingbias voltage generator means for defining the duration of the controlpulses as a function of the amplitude of the bias voltage; and fuelinjection means connected between the control pulse generator means andthe engine for applying fuel to the engine for the duration of each ofthe control pulses; the combination comprising: speed voltage generatormeans connected to the control pulse generator means for producing aspeed voltage having an amplitude which unidirectionally varies from abase level at the termination of each preceding control pulse to a peaklevel at the initiation of each succeeding control pulse; and meansconnected between the speed voltage generator means and the bias voltagegenerator means for maintaining the amplitude of the bias voltagesubstantially constant at a level proportional to the peak level of thespeed voltage thereby to define the duration of the control pulses inresponse to the speed of the engine.
 2. In an internal combustion enginesystem including control pulse generator means for producing controlpulses at a frequency proportional to the speed of the engine, thecontrol pulse generator means including bias voltage generator means fordefining the duration of the control pulses as a function of theamplitude of a bias voltage; and fuel injection means connected betweenthe control pulse generator means and the engine for applying fuel tothe engine for the duration of each of the control pulses; thecombination comprising: speed voltage generator means connected to thecontrol pulse generator means for producing a speed voltage havingsuccessive cycles during which the amplitude of the speed voltageunidirectionally varies from a base level at the termination of eachpreceding control pulse to a peak level at the initiation of eachsucceeding control pulse; compensation voltage generator means connectedto the speed voltage generator means for producing a compensationvoltage having an amplitude which is substantially constant over theduration of each succeeding control pulse at a level proportional to thepeak level of the speed voltage during each preceding cycle; and biasvoltage modifier means connected between the compensation voltagegenerator means and the bias voltage generator means for defining theamplitude of the bias voltage as a function of the amplitude of thecompensation voltage thereby to determine the duration of the controlpulses in response to the speed of the engine.
 3. In an internalcombustion engine system including control pulse generator means forproducing control pulses in synchronization with the speed of theengine, the control pulse generator means including bias voltagegenerator means for defining the duration of the control pulses as afunction of the amplitude of a bias voltage; and fuel injection meansconnected between the contrOl pulse generator means and the engine forapplying fuel to the engine for the duration of each of the controlpulses; the combination comprising: speed voltage generator meansconnected to the control pulse generator means for producing a speedvoltage which varies from a base level at the termination of eachpreceding control pulse, the speed voltage generator means including anRC network having a time constant for defining the amplitude of thespeed voltage in accordance with the time constant which is relativelyshort compared to the shortest duration between each of the controlpulses; compensation voltage generator means connected to the speedvoltage generator means for producing a compensation voltage whichvaries from a base level proportional to the peak level of the speedvoltage at the initiation of each succeeding control pulse, thecompensation voltage generator means including an RC network having atime constant for defining the amplitude of the compensation voltage inaccordance with the time constant which is relatively long compared tothe longest duration of each of the control pulses; and bias voltagemodifier means connected between the compensation voltage generatormeans and the bias voltage generator means for controlling the amplitudeof the bias voltage in response to the amplitude of the compensationvoltage thereby to define the duration of the control pulses as afunction of the speed of the engine.
 4. In an internal combustion enginesystem including control pulse generator means for producing controlpulses at a frequency proportional to the speed of the engine, thecontrol pulse generator means including bias voltage generator means fordefining the duration of each of the control pulses as a function of thelevel of the bias voltage; and fuel injection means connected betweenthe control pulse generator means and the engine for applying fuel tothe engine for the duration of each of the control pulse; thecombination comprising: speed voltage generator means connected to thecontrol pulse generator means for producing a speed voltage which variesfrom a base level at the termination of each preceding control pulse toa peak level at the initiation of each succeeding control pulse so thatthe peak level of the speed voltage is inversely related to the speed ofthe engine, the speed voltage generator means including an RC networkhaving a time constant for defining the amplitude of the speed voltagesuch that the peak level occurs at an upper potential when the enginespeed is at a lower limit and occurs at a lower potential when theengine speed is at an upper limit; compensation voltage generator meansconnected to the speed voltage generator means for producing acompensation voltage which varies from a base level at the initiation ofeach succeeding control pulse, the compensation voltage generator meansincluding a voltage level converter for defining the base level of thecompensation voltage relative to a maximum potential and a minimumpotential as the peak level of the speed voltage is defined relative tothe upper potential and the lower potential, the compensation voltagegenerator means further including an RC network having a time constantfor defining the amplitude of the compensation voltage substantiallyconstant at the base level over the duration of each succeeding controlpulse; and bias voltage modifier means connected between thecompensation voltage generator means and the bias voltage generatormeans for shifting the amplitude of the bias voltage in proportion tothe amplitude of the compensation voltage thereby to define the durationof the control pulses as a function of the speed of the engine.
 5. In aninternal combustion engine system including control pulse generatormeans for producing control pulses at a frequency proportional to thespeed of the engine, the control pulse generator means including biasvoltage generator means for defining the duration of the control pulsesas a function of the ampLitude of a bias voltage; and fuel injectionmeans connected between the control pulse generator means and the enginefor applying fuel to the engine for the duration of each of the controlpulses; the combination comprising: speed voltage generator meansconnected to the control pulse generator means and including a capacitorfor developing a speed voltage thereacross, discharging means connectedto the capacitor for discharging the capacitor from the initiation ofeach preceding control pulse until the termination of each precedingcontrol pulse to clamp the speed voltage at a base level, and chargingmeans connected to the capacitor for charging the capacitor from thetermination of each preceding control pulse to the initiation of eachsucceeding control pulse according to a relatively short time constantto increase the speed voltage from the base level to a peak level whichis at an upper potential when the engine speed is at a low limit andwhich is at a lower potential when the engine speed is at a high limit;compensation voltage generator means connected to the speed voltagegenerator means and including a capacitor for developing a compensationvoltage thereacross, charging means connected to the capacitor forcharging the capacitor from the termination of each preceding controlpulse until the initiation of each succeeding control pulse to clamp thecompensation voltage at a base level defined relative to a maximumpotential and a minimum potential as the peak level of the speed voltageis defined relative to the upper potential and the lower potential, anddischarging means connected to the capacitor for continually dischargingthe capacitor according to a relatively long time constant to maintainthe compensation voltage substantially constant at the base level overthe duration of each succeeding control pulse; and the bias voltagemodifier means connected between the compensation voltage generatormeans and the bias voltage generator means for defining the amplitude ofthe bias voltage in response to the amplitude of the compensationvoltage thereby to determine the duration of the control pulses as afunction of engine speed.